Why an older company may show a different number
Before the reform, a business held three separate documents: a business licence from the industry and commerce authority, an organisation code certificate, and a tax registration certificate. The "three-in-one, one licence one code" (三证合一、一照一码) reform took effect on 1 October 2015 and replaced all three with a single licence carrying the Unified Social Credit Code. The changeover ran to the end of 2017, with limited cases extended to 2020. If a counterparty sends a document showing a 15-digit registration number, it predates the reform, and you should ask for the current licence.
One number, two systems
Registry and taxThe same code identifies the company at the market regulation authority (SAMR) and at the tax bureau. You do not need a separate taxpayer number to check an invoice against an entity.